This invention relates to bottom supported steam generators for burning solid fuel and in particular to an integral economizer arrangement therewith.
The burning of solid fuels in a steam generator yields a solid ash. At least a portion of this ash is carried with the flue gases past the tubing surfaces and through the ducts. These ash particles cause erosion on the surfaces and settle out at various locations with resultant plugging of the gas flow path.
Most boiler designs for burning solid fuels are top supported with separate grid steel or else they are bottom supported with the baffled steam generating bank. The baffled bank is a source of rapid tube erosion due to the abrasive action of the ash particles carried through the boiler by the flue gas.
Baffling of the steam generating bank produces cross flow of the gases across the tubes thereby increasing the heat transfer rates. This results in the smallest amount of tubing required; and, accordingly, the water drum for the convection bank tends to be supported at an intermediate elevation. The flowing gases must then be conducted outside of the steam generating area to an economizer. Furthermore, experience has shown that horizontal gas flow through economizers tends to result in ash build up and blockage of the tubes. Accordingly, additional ducting is required to achieve vertical downflow through an externally located economizer.